1. Field of the Invention
The present invention relates to porous materials that can be used as adsorption materials for concentration of organic substances and/or separation of undesired substances, and as catalyst materials for selective catalytic reactions. The porous materials comprise organic groups integrated into the inorganic porous structure.
2. Description of the Related Art
Known mesoporous molecular sieves (hereinafter, referred to as mesoporous materials) consist of an inorganic oxide porous substance and have a pore diameter of 1.5 to 30 nm, which is larger than known zeolite pore diameters. The pore size distribution is generally uniform and the pores are regularly arranged. The pore structure of such mesoporous materials is large enough to absorb large molecules and the pore wall structure can be as thin as about 1 nm. Further, such mesoporous materials are known to have large specific surface areas (about 1000 m.sup.2 /g) and large pore volumes (about 1 cc/g). For these reasons, such the mesoporous materials enable reactive catalysts, adsorbents composed of a functional organic compound and other molecules to rapidly diffuse into the pores and are therefore, advantageous over zeolites, which have smaller pore sizes. Consequently, such mesoporous materials have been used in high-speed catalytic reactions that require fast reactions and as large capacity adsorbents, which are capable of adsorbing a large amount of an adsorbing material.
Examples of such mesoporous materials are FSM-16 (T. Yanagisawa et al., Bull. Chem. Soc., Jpn., 63,988 (1990), S. Inagaki et al., J. Chem. Soc., Chem. Commun., 680 (1993)) and the M41Ss (e.g., MCM-41, MCM-48) (C. T. Kresge et al., Nature, 359,710 (1992), J. S. Beck et al., J. Am. Chem. Soc., 114, 10834 (1992)).
PCT publication No. WO9834723 describes trials that were conducted in which an organic group was attached onto the surface of an inorganic skeleton of these mesoporous materials, namely onto the inner surface of a pore, so as to impart a selective adsorption ability and specific catalyst function to the mesoporous substance. Another trial was conducted in which organic groups were introduced during the synthesis the mesoporous material. Such mesoporous materials were formed with organic groups bound as side chains to the base skeleton made of the inorganic material. Specifically, the organic groups were suspended from the surface of the base skeleton made of the inorganic material. Consequently, the pore wall was basically composed of a skeleton made of inorganic materials and the organic groups project from the surface of the pore wall to form a layer composed of the organic groups.
In such a structure, the surface characteristics of the porous material may be determined by the characteristics of the organic groups. As a result, such porous materials were restricted to adsorbing substances to which the organic groups have affinities. Further, catalytic function or adsorption function derived from the inorganic skeleton can be masked, because the catalytic active sites or adsorption sites in the inorganic skeleton are covered by the organic groups.
The thickness of the pore wall also may increase corresponding to the introduction of the organic group, and substantial decreases in pore diameter and pore volume may result. Further, such organic groups may release under high temperatures or in a catalytic reaction and adsorption reaction, thus leading to the loss of desirable surface properties and the contamination of the treated material by the released organic group.